As an emerging photoelectric material, perovskite has evoked widespread scientific and industrial interests due to its versatile applications in solar cells, light-emitting diodes, laser diodes, photodetectors, and thin film photovoltaics. This material is an organic-inorganic trihalide perovskite with an ABX3 structure (where A is an organic or monovalent alkali cation, B a divalent metal ion and each X a halide such as chlorine (Cl), bromine (Br) or iodine (I)). A typical and well-known perovskite compound is methylammonium lead triiodide (CH3NH3PbI3), which can be synthesized from cheap materials, in contrast to traditional semiconductors. Various deposition procedures can be employed to fabricate perovskite thin films including simple one-step solution coating, sequential dip coating, vacuum thermal co-evaporation deposition and vapor-assisted solution processes. Taking perovskite solar cells as an example, perovskite thin films exhibit excellent crystallinity, ambipolar transport and large diffusion length for both electrons and holes, which boost the power conversion efficiencies (PCEs) of devices exceeding 16% in planar heterojunction and mesoporous device architectures.
Although the device efficiency of perovskite photovoltaic has constantly been improved in the past few years through optimizing device design, material interfaces and processing techniques, the basic properties of organic-inorganic trihalide perovskites are not well understood. Cavities or pinholes can be found in solution-processed perovskite thin films fabricated with aforementioned methods, and these can cause shunting pathways thereby degrading device performance.
Therefore, it remains a challenge to obtain high quality and continuous perovskite thin films with good uniformity, high coverage rate and large grain size on top of polymer or metal oxide charge transport layers in a photovoltaic device.